The present invention relates to an image forming apparatus to form an image onto a recording sheet, and particularly, to a sheet feeding control technology in the image forming apparatus.
In the image forming apparatus to form an image by an electro-photographic method, inkjet method, or heat sensitive method, as a technology to shorten the time necessary for forming one sheet of an image, there are a means to increase the conveying speed of the recording sheet in the image forming process, and a means to shorten an interval between the conveying start times of the preceding conveyed recording sheet and the following conveyed recording sheet, that is, to shorten the sheet feed interval.
As one of specifications of the image forming apparatus, there is CPM (Copy Per Minute) or PPM (Print Per Minute). The number of sheets on which the image can be formed onto A4 sized recording sheets in the continuous image formation for one minute are used in many cases for the CPM or PPM. Hereinafter, the CPM and PPM are generally called the image forming speed.
In the development of the image forming apparatus, initially a target image forming speed is set, and each condition of each section of the image forming apparatus or image forming process is designed so that the target image forming speed can be attained.
In this connection, although the image forming speed is determined by the conveying speed of the recording sheet in the image forming process, in many image forming apparatus, as the conveying speed, the lower value as possible is used. Accordingly, the sheet feed interval is set to a value which is shortened to the limit.
This is for the reason why the conveying speed relates to the moving speed of a photoreceptor, the writing speed of the image, and the operation speed of the whole image forming apparatus including the fixing speed, and because the increase of the conveying speed is the increase of the operation speed of the whole image forming apparatus, from the view points of cost reduction or the assurance of the stability of the operation, it is preferable that the conveying speed is set lower.
However, in the conventional technology, because it is difficult that the sheet feed interval is shortened more than a certain time, a case where the target image forming speed can not be attained, or a case where it is necessary to adopt a means by which the conveying speed is increased in order to attain the target image forming speed, is generated. As described above, in order to attain the target image forming speed, when the means by which the conveying speed is increased is adopted, it is not preferable because the operation speed of whole the image forming apparatus is increased.
Particularly, in the improvement to increase the image forming speed in the partial improvement when the improved machine of the machine which is provided in the market is developed, because the improvement method of the image forming speed by the shortening of the sheet feed interval can not be adopted, there are many cases where it is difficult that the target image forming speed is attained.
An object of the present invention is to solve the above described problems in the conventional technology to increase the image forming speed, and to provide an image forming apparatus in which the conveying speed is set to a low value and further the high image forming speed is shown, and a sheet feed method in the image forming apparatus.
The object of the present invention can be attained by any one of the following Structures (1)-(8).
(1) An image forming apparatus which has the primary sheet feed means, and secondary sheet feed means for conveying the recording sheet which is fed from the primary sheet feed means to the image forming position in timed relationship with the image formation, and a control means for controlling the primary sheet feed means and the secondary sheet feed means, the image forming apparatus is characterized in that: the control means selects the long and short two kind of sheet feed intervals according to the detection signal of a recording sheet detection means provided at the upstream of the secondary sheet feed means in the control.
(2) An image forming apparatus according to the above (1), wherein the control means conduct the control by using a short sheet feed interval when it is detected that the recording sheet is fed at the arrival time within the range of a portion of a faster side in the fluctuation of the secondary sheet feed arrival time at which the recording sheet arrives at the secondary sheet feed means, and conducts the control by using a long sheet feed interval when the recording sheet is fed at the arrival time outside said range of the portion of the faster side and within a range of allowable fluctuation.
(3) An image forming apparatus according to the above (1) or (2), wherein the control means conducts the control so that the integer value in which the image forming speed calculated from the two kind of sheet feed intervals is rounded to the nearest whole number, coincides with the target image forming speed value.
(4) An image forming apparatus according to any one of the above (1) to (3), wherein the control means controls the secondary sheet feed means so that the recording sheet is fed at the two kind of the sheet feed intervals, and controls the first sheet feed means on the basis of the control of the secondary sheet feed means.
(5) A sheet feed method in the image forming apparatus in which the recording sheet is conveyed from the accommodation means by the primary sheet feed means to the secondary sheet feed means, and the recording sheet is fed to the image forming position by being conveyed by the secondary sheet feed means, the sheet feed method in the image forming apparatus is characterized in that: as the sheet feed interval when the recording sheet is fed to the image forming position, the long and short two kind of sheet feed intervals are used, and when the recording sheet is fed at the arrival time within the range of a portion of a faster side in the fluctuation of the arrival time at which the recording sheet arrives at the secondary sheet feed means, the recording sheet is fed at the short sheet feed interval, and when the recording sheet is fed at the arrival time outside said range of the portion of the faster side and within the allowable fluctuation range, the secondary sheet feed means conducts the sheet feed at the long sheet feed interval.
(6) A sheet feed method in the image forming apparatus according to the above (5), wherein the leading edge of the recording sheet is detected on the upstream side of the secondary sheet feed means, and by the control according to the leading edge detection signal, the secondary sheet feed means conducts the sheet feed.
(7) A sheet feed method in the image forming apparatus according to the above (5) or (6), wherein the primary sheet feed means conducts the sheet feeding according to the detection signal.
(8) A sheet feed method in the image forming apparatus according to any one of the above (5) to (7), wherein the primary sheet feed means operates on the basis of the operation of the secondary sheet feed means.